[Bug]: OpenGL context drawn in wrong position when using client-side decorations (GNOME)

[ollpu]

Detailed steps on how to reproduce the bug

Run any of the OpenGL demos under GNOME. You will notice that the OpenGL context is drawn in the wrong place, on top of other elements:

Mouse events are still recognized in the original positions, so I have to click a little lower than where the dropdown appears, for example.

There is also something wrong with the text box, but this issue is not about that.

What is the expected behaviour?

GL context drawn in proper location, as on other platforms.

Works fine on some other desktops, such as KDE Plasma and Cinnamon. This leads me to believe the issue is caused by client side decorations (CSD) which GNOME uses: the surface of the X11 window includes the top bar, but this is not accounted for correctly when the subwindow is spawned.

Operating systems

Linux

What versions of the operating systems?

NixOS 25.05
GNOME 48 (Wayland or X11)
Linux 6.12.51

Architectures

x86_64

Stacktrace

Plug-in formats (if applicable)

Standalone

Plug-in host applications (DAWs) (if applicable)

No response

Testing on the develop branch

The bug is present on the develop branch

Code of Conduct

• I agree to follow the Code of Conduct

[ollpu]

Interestingly, the issue persists if I set setUsingNativeTitleBar(false). Broken on GNOME, correct on KDE.